Question

I’m selecting products from a database table. Currently the query is launched from Coldfusion, where I have an “optional LEFT JOIN” like so:

SELECT a.products
FROM artikelstammdaten a
  <cfif modul_aktiv("preorder", my_module) IS "true">
     LEFT JOIN...
  </cfif>
WHERE ...

Question:
Is it possible to do an optional LEFT JOIN in MySQL. I’m thinking something like this:

SELECT a.products
FROM artikelstammdaten a
    AND ( 
        ((param_preorder = 'false') "(1=2)" )
          OR LEFT JOIN ...  
        )
WHERE ...

Answer 1

Well, you can do something like this:

SELECT a.products
FROM artikelstammdaten a
LEFT JOIN [another_table] ON [your parameterized condition] AND [the real join condition]
(...)

The LEFT JOIN will be done, whatever your condition is, but if it is false, it won’t bring back any record.

But you certainly can’t emulate the cfif in pure SQL 🙂